1. Field of the Invention
The present invention relates to a CCD (Charge Coupled Device) solid-state image pickup device and a method of driving such an image pickup device.
2. Description of the Related Art
A CCD solid-state image pickup device is, as described, e.g., in JP-A-2000-350099, provided with vertical charge-transfer channels (VCCDs) and a horizontal charge-transfer channel (HCCD), and configured so that signal charges read out from photodiodes (photoelectric conversion elements) formed in a two-dimensional, array on a semiconductor substrate surface to the vertical charge-transfer channels are transferred first to the horizontal charge-transfer channel along the vertical charge-transfer channels and then transferred into a charge detection section and an output amplifier along the horizontal charge-transfer channel, and the output amplifier puts out the signals of voltage values respectively responsive to amounts of the signal charges transferred into the charge detection section.
A timing chart showing the related-art transfer timing of signal charges is illustrated in FIG. 3. Transfers of signal charges in a vertical direction are performed by application of vertical transfer pulses φV1, φV2, φV3 and φV4 to vertical charge-transfer channels, and transfer of signal charges in a horizontal direction is performed by application of horizontal transfer pulses φH1 and φH2 to the horizontal charge-transfer channel.
When the vertical transfer pulses φV1, φV2, φV3 and φV4 are applied to each of the vertical charge-transfer channels, charges detected by photodiodes horizontally aligned in a row on a semiconductor substrate are each transferred vertically by one step, and accumulated on a line memory (LM) for buffer use which is provided between the end of each vertical charge-transfer channel and the horizontal charge-transfer channel.
And, when a driving pulse φLM is applied to the line memory, the signal charges on the line memory are transferred to the horizontal charge-transfer channel. Then, two-phase driving pulses φH1 and φH2 are applied to the horizontal charge-transfer channel, all the signal charges on the horizontal charge-transfer channel are read out by the output amplifier, and thereafter the next row of signal charges are transferred in the vertical direction.
More specifically, each of image pickup devices hitherto known is configured so that the horizontal charge-transfer channel is driven during horizontal transfer periods (output periods) and the vertical charge-transfer channels and the line memory are driven during horizontal blanking periods when the driving of the horizontal charge-transfer channel is stopped. This is because, when the vertical charge-transfer channels are driven during the horizontal transfer periods (when rise timing and fall timing of vertical transfer pulses φV1, φV2, φV3 and φV4 overlap with the horizontal transfer periods), influence of noises develops on the output side.
In the related-art CCD solid-state image pickup devices, as mentioned above, vertical transfers are performed during periods not overlapping with horizontal transfer periods, and thereby mixing of noises is avoided. In other words, the related-art CCD solid-state image pickup devices have a problem that it is impossible to drive them at a high speed since vertical transfers cannot be performed during horizontal transfer periods.